1. Field of Invention
The present invention relates to an improved organo-refining process to produce low ash clean coal from high ash coals used for metallurgical applications.
2. Description of Related Art
The existing process to produce low ash clean coal from high ash coals comprises a step of chemical beneficiation of the coal by dissolving organic matter of coal in various organic solvents. As the coal basically constitutes a heterogeneous mixture of organic and inorganic constituents, a process of solvolysis of coal varies depending on its constituents, maturity and structural characteristics. The main advantages of the chemical benefication process are i) ease of recovery of the solvent from the main process stream, ii) solvolytic efficiency of the recovered solvents is as high as that of a fresh solvent, iii) 95-98% recovery of the solvent, iv) improved coking properties of clean coal, and v) availability of industrial organic solvents. However, the operating cost of this process is substantially high because of high cost of the solvents and energy requirement in the process.
Organo-refining, or solvent-refining, or, solvent extraction of coal is a well-known process technology. However, the primary objective in most of the existing processes is to produce ultra clean coal or super clean coal with ash contains less than 4%. Incidentally, the average content of this parent coal (Run of Mine) is 25%. Exploratory study revealed that it is possible to extract at least 50% of the parent coal through this studied process of extraction albeit under reflux conditions at atmospheric pressure. The processed coal contains almost 4% ash.
The yield and the ash content of the super clean coal when produced by the studied process as described hereinabove, is also observed to be satisfactory. In a bench scale set up to carry-out the studied process, the main concerning factor apart from yield is the economic viability of the studied process, for example, a substantially higher consumption of heat for extraction. Again, recovery of the solvent has warrants high consumption of heat. Combination of the above two heat inputs prima-facie drives the studied process towards infeasibility. Now, if the two heat consumptions are arranged on priority basis, then heat consumption for the extraction supersedes, as the extraction process solely depends upon the extraction temperature, this is why it is often called as thermal extraction. Thus, the heat requirement for solvent recovery is the only possibility for minimization of total heat consumption. Accordingly, an effective or optimized design of solvent recovery could convert the studied process as a feasible one.